1. Technical Field
This invention relates to precast concrete roadway-dividing wall sections and particularly to asymmetrical wall sections for dividing roadways having different grade levels and different slopes from one end of the section to the other end.
2. Background Art
The superior effectiveness of contoured concrete roadway dividing walls of the so-called New Jersey type in preventing accidents and mitigating the damage when accidents do occur has led to increasing use of these walls as replacements for metal guard rails or median strips in highway modernization programs as well as in new highway construction. The New Jersey type barrier wall has a scientifically developed contour consisting of a low vertical base segment (about three inches high), an intermediate inwardly sloping segment, and an upper segment of less inward slope than the intermediate segment. The latter two segments have specified angles and heights that function with the low base segment to effectively redirect a vehicle coming into contact with the wall back into the roadway, minimizing the tendency to climb the wall, overturn, or ricochet into another lane.
Although mobile adjustable form equipment is available for on-site pouring of such walls in a continuous line, most dividers are made up of precast concrete sections, which are typically twenty feet long. When the roadways on both sides of a dividing wall are at the same grade, symmetrical precast sections of standard dimensions can be used. Often, however, the roadways are at substantially different levels, particularly on curves, and the difference in level can change along the twenty foot length of a section. Since the profile on each side of the wall must follow the roadway on that side, an asymmetrical barrier is required in such a situation. Each section must be custom designed to have vertical differences as specified in the construction plans at each end between corresponding segments of the opposite contoured profiles.
U.S. Pat. No. Re. 32,936 of the present inventor discloses an adjustable mold for asymmetrical barrier sections. This mold is quickly adjustable to specified differences in height and slope of the contoured faces on each side to enable pouring of a monolithic asymmetrical barrier section and has pivoted sides and hinged ends so that the section can be removed from the mold easily after it has cured. The mold is very large and expensive, however, compared with a standard symmetrical barrier mold, and the resulting custom cast sections are necessarily more expensive than standard symmetrical sections.
The prior art practice of providing monolithic precast asymmetrical wall sections has other inherent drawbacks. Because of the vertical offset between the two sides, precast asymmetrical wall sections are significantly higher and heavier than standard symmetrical sections. This means fewer sections per truckload. Because of their individual differing dimensions, they cannot be cross-stacked like standard symmetrical sections, so they require more storage area at the precasting plant and at the job site.
In some instances where there is sufficient median space, New Jersey type barriers have been installed using precast half-sections facing lanes of oppositely moving traffic. The half-sections are spaced apart by a substantial distance (e.g., several feet), with the intervening space backfilled and covered with blacktop or concrete to protect against water washing away the backfill material. In these installations, the opposed half-sections are essentially independent retaining walls, so each line of half-sections can follow the grade of the respective adjacent roadway. Because the half-sections are identical, there can result a vertical difference between the tops of the sections that creates an uneven top surface of the barrier. Settling of the backfill can also cause the protective blacktop or concrete layer to crack, allowing water to enter the backfilled space. The backfilled space also reduces the area available for shoulders or possible additional traffic lanes.
Under current economic conditions, it is often necessary to rebuild or rehabilitate a highway system in stages, as funds become available. The need for safe, effective, and often asymmetric, barriers may exist for each construction stage, even though short lived. To provide space-saving, monolithic site-specific asymmetrical barrier sections for one stage that may need to be changed for the next stage is cost prohibitive. There is a need, therefore, to provide asymmetric barrier sections which may be easily and economically adjusted and made site-specific for each stage. The present invention provides such a system.